Tire

ABSTRACT

Provided is a tire exhibiting improved wear resistance, partial wear resistance, and traction performance on the wet road surface. The tire has block land portion arrays  5  defined on a tread portion  1 . Between two block land portion arrays  5  located adjacent to each other while sandwiching a circumferential groove  2 , a block land portions  4  constituting the block land portion arrays are arrange so as to be positionally displaced from each other, and a groove portion  6  located between the block land portions adjacent in the tire width direction extends obliquely with respect to tire width direction and the tire circumferential direction. At this time, a distance d 2  between the block land portions adjacent in the tire width direction is shorter than a distance d 1  between the block land portions adjacent in the circumferential direction. In the block land portion arrays  5  adjacent in the tire width direction, an inclined angle α of a side wall  9  of the block land portion  4  located on the groove portion  6  side with respect to the tire circumferential direction is larger than an inclined angle β of the other side wall  10  located on the opposite side to said groove portion  6  with respect to the tire circumferential direction.

TECHNICAL FIELD

The present invention relates to a tire having, on a tread portion,plural tire-circumferential grooves extending in a tire circumferentialdirection, and plural lateral grooves each communicating adjacent twotire-circumferential grooves, thereby to define plural block landportion arrays formed by a large number of block land portions, and inparticular, to a tire for heavy load, aimed at improving partial wearresistance and traction performance on a wet road surface whileimproving wear resistance of the tire.

RELATED ART

In general, a tire for heavy load is designed to have a high aspectratio and high belt rigidity of the tire so as to be able to bearconsiderable amount of weight. Further, in many cases, the tire forheavy load is designed to have a tread pattern in which block landportions are arranged over the entire tread portion so as to be able totravel under various traveling conditions.

The tire for heavy load having such a pattern can bear heavier load ascompared with tires for general vehicles, and hence, partial wearresulting from heel and toe wear is likely to occur during travel inproportion to the amount of load that the tire bears. The heel and toewear refers to wear in which, due to excess deformation of block landportions at the time when the tire is rotated with load, a wear amountof a leading edge (portion that first comes into contact with theground) of the tire is smaller, and the wear amount of a trailing edge(portion that finally comes into contact with the ground) of the tire inthe tire circumferential direction is larger. As a result, there occursa difference in wear mainly between both edges of the block land portionin the tire circumferential direction, reducing the lifetime of the tirein terms of wear.

Conventionally, for the problem of partial wear as described above,various countermeasures for suppressing the partial wear have beenattempted. Of the countermeasure, as disclosed in Patent Document 1 forexample, there is proposed an effective method for preventing thepartial wear resulting from collapsing deformation, which includes:reducing a depth of a part of lateral grooves defining a block, in otherwords, forming a bottom-raised portion in each of the lateral grooves tostrengthen stress against collapsing deformation of the block landportion toward the tire circumferential direction so as to suppressincrease in the driving force per unit area that the tread portion hasto bear.

RELATED ART DOCUMENT Patent Document

-   Patent Document 1: Japanese Patent Application Laid-open No.    6-171318

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Tires for heavy load for used in trucks or buses have a high aspectratio and high belt rigidity. Thus, at the time when the tire is rotatedwith load, there occurs friction between a belt portion, which isrotated by driving force, and a tread portion, which is in contact withthe ground, generating a difference in deformation between the beltportion and the tread portion as illustrated in FIG. 1, thereby causingexcessive collapse and deformation at the tread portion. This increasesthe amount of driving force per unit area that the tread portion has tobear, and sliding phenomenon occurs between a block land portion and theground, causing an increase in the amount of wear of the block landportion. Although a tire described in Patent Document 1 can produce aneffect of preventing the partial wear on a certain level, there is ademand for further improving the effect of preventing the partial wearfrom the viewpoint of increase in tire lifetime. Further, PatentDocument 1 cannot sufficiently suppress collapsing and deformation ofthe block land portion at the time of tire rotation with load.Therefore, the tire described in Patent Document 1 cannot suppress theincrease in the amount of wear of the block land portion caused by thesliding phenomenon, and a problem of wear resistance is left unsolved.Further, in general, it is possible to effectively suppress the amountof wear of the block land portion, by increasing the rigidity of arubber forming the block land portion to suppress the excess collapsingand deformation of the block land portion. However, this excessivelyincreases the rigidity of the block land portion, possibly causing theblock land portion to break due to chip or crack at the time when thetire is rotated with load. Yet further, for such a tire, sufficientattention has not been paid to the traction performance on the wet roadsurface, and in recent years, there is a demand for improvement in thetraveling safety, whereby improvement for traction performance on thewet road surface is further required for the tires.

In view of the facts described above, an object of the present inventionis to provide a tire exhibiting improved partial wear resistance andtraction performance on a wet road surface while improving wearresistance, by optimizing shapes of block land portions and itspositional arrangement.

Means for Solving the Problem

In order to achieve the object above, the present invention provides atire having, on a tread portion, a plurality of circumferential groovesextending in a tire circumferential direction, and plural lateralgrooves each communicating adjacent two circumferential grooves, therebydefining a plurality of block land portion arrays formed by a largenumber of block land portions, wherein: between block land portionarrays adjacent to each other while sandwiching the circumferentialgroove, the block land portions constituting said block land portionarrays are arranged so as to be positionally displaced from each otherin the tire circumferential direction; a groove portion between theblock land portions adjacent in the tire width direction extendsobliquely with respect to the tire width direction and the tirecircumferential direction; a distance between the block land portionsadjacent in the tire width direction is shorter than a distance betweenthe block land portions adjacent in the tire circumferential direction;a length of the block land portion in the widthwise cross section of thetire increases from both edge portions of the block land portion in thecircumferential direction toward a central portion of the block landportion; and, of side walls of the block land portion in block landportion arrays adjacent in the tire width direction, an inclined angleof a side wall located on the groove portion side between the block landportions adjacent in the tire width direction with respect to the tirecircumferential direction is larger than an inclined angle of the otherside wall located on the opposite side to said groove portion as viewedfrom the tire width direction with respect to the tire circumferentialdirection. In this specification, the “groove portion” represents aportion of the circumferential groove, and means a groove extendingbetween the block land portions adjacent in the tire width direction;the expression “positionally displaced” means arrangement in whichbeginning points of the respective block land portions adjacent in thetire width direction are arranged differently from each other at pitchesin the tire circumferential direction, so that edges of block landportions in the circumferential direction are different between theblock land portions adjacent in the tire width direction. Further, the“central portion of the block land portion” means a portion extendingfrom the central position of the block land portion in the tirecircumferential direction toward both edges of the block land portion upto the range of 40% of the length of the block land portion in the tirecircumferential direction, and, more specifically, means an area inwhich 30% from the respective edge portion of the block land portion inthe circumferential direction is excluded.

Further, it is preferable that an inclined angle of the side walllocated on the outside of the block land portion in the tire widthdirection with respect to the tire circumferential direction is in therange of 0 to 30°.

Yet further, it is preferable that a ratio of a distance between theblock land portions adjacent in the tire circumferential direction withrespect to a distance between the block land portions adjacent in thetire width direction is in the range of 1:0.85 to 1:0.3.

Still yet further, it is preferable that a ratio of a length of theblock land portion in the tire circumferential direction with respect toa distance between the block land portions adjacent in the tirecircumferential direction is in the range of 1:0.25 to 1:0.05.

Still yet further, it is preferable that the distance between the blockland portions adjacent in the tire width direction is in the range of1.0 to 5.0 mm.

Still yet further, it is preferable that the distance between the blockland portions adjacent in the tire circumferential direction is in therange of 3.0 to 10.0 mm.

Still yet further, it is preferable that the block land portion isprovided with a narrow groove communicating two circumferential groovesadjacent in said block land portion in the tire width direction.

Still yet further, it is preferable that the narrow groove is open tothe circumferential groove at the central portion of the block landportion.

Still yet further, it is preferable that the length of the narrow groovein the tire circumferential direction is in the range of 5 to 20% of adepth of the lateral groove.

EFFECT OF THE INVENTION

According to the present invention, it is possible to provided a tireexhibiting improved partial wear resistance and traction performance onthe wet road surface while improving wear resistance, by optimizing theshapes of the block land portions and arrangement thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a relationship between thepresence/absence of a load by driving force and positions to which atread portion moves.

FIG. 2 is a development view illustrating a portion of a typical treadportion of a tire according to the present invention.

FIG. 3 is a perspective view of a block land portion illustrated in FIG.2 (reference character T: deformation of rubber from a trailing edgetoward a leading edge due to pressing in the oblique direction).

FIG. 4 is a diagram illustrating a shearing force from a road surfacewhen driving force is applied

FIG. 5 is a diagram illustrating deformation of adjacent block landportions when the driving force is applied.

FIG. 6 is a diagram illustrating deformation of the block land portionswhen block land portions adjacent in the tire circumferential directionare excessively closed to each other.

FIG. 7( a) is a diagram illustrating a block land portion that ispressed against and is in contact with the road surface in a horizontalmanner, and FIG. 7( b) is a diagram illustrating a block land portionthat is pressed against and is in contact with the road surface in anoblique manner.

FIG. 8 is a diagram illustrating deformation of an adjacent block landportion when driving force is applied. (reference character α: increasein shearing deformation at a step-in time, reference character β:increase in the amount of rise, and reference character γ: decrease indeformation of the tread rubber toward a direction opposite to arotational direction)

FIG. 9 is a development view illustrating a part of another treadportion of the tire according to the present invention.

FIG. 10 is a development view illustrating a part of another treadportion of the tire according to the present invention.

FIG. 11 is a development view illustrating a part of another treadportion of the tire according to the present invention.

FIG. 12 is a development view illustrating a part of another treadportion of the tire according to the present invention.

FIG. 13 is a development view illustrating a part of another treadportion of the tire according to the present invention.

FIG. 14 is a development view illustrating a part of another treadportion of the tire according to the present invention.

FIG. 15 is a development view illustrating a part of a tread of aConventional Example tire.

FIG. 16 is a development view illustrating a part of a tread of aComparative Example tire 1.

FIG. 17 is a development view illustrating a part of a tread of aComparative Example tire 2.

FIG. 18 is a development view illustrating a part of a tread of aComparative Example tire 3.

FIG. 19 is a development view illustrating a part of a tread of aComparative Example tire 4.

FIG. 20 is a development view illustrating a part of a tread of aComparative Example tire 5.

FIG. 21 is a development view illustrating a part of a tread of aComparative Example tire 6.

FIG. 22 is a development view illustrating a part of a tread of aComparative Example tire 7.

FIG. 23 is a development view illustrating a part of a tread of aComparative Example tire 8.

FIG. 24 is a development view illustrating a part of a tread of aComparative Example tire 9.

FIG. 25 is a development view illustrating a part of a tread of anExample tire 2.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, an embodiment of the present invention will be describedwith reference to the drawings. FIG. 2 is a development viewillustrating a portion of a typical tread portion of a tire according tothe present invention. FIG. 3 is a perspective view of a block landportion illustrated in FIG. 2. FIG. 4 is a diagram illustrating ashearing force from a road surface when driving force is applied. FIG. 5is a diagram illustrating deformation of adjacent block land portionswhen the driving force is applied. FIG. 6 is a diagram illustratingdeformation of the block land portion when block land portions adjacentin the tire circumferential direction are excessively close to eachother. FIG. 7( a) is a diagram illustrating a block land portion that ispressed against and is in contact with the road surface in a horizontalmanner. FIG. 7( b) is a diagram illustrating a block land portion thatis pressed against and is in contact with the road surface in an obliquemanner. FIG. 8 is a diagram illustrating deformation of an adjacentblock land portion when driving force is applied. FIGS. 9 to 14 aredevelopment views each illustrating a part of other tread portion of thetire according to the present invention.

In the present invention, as illustrated in FIG. 2, a tire has, on atread portion 1, plural circumferential grooves 2 extending in acircumferential direction of the tire and plural lateral grooves 3 eachcommunicating two adjacent circumferential grooves 2, thereby to defineplural block land portion arrays 5 formed by a large number of blockland portions 4. Further, between adjacent block land portion arrays 5,5, the block land portions 4 constituting the block land portions arearranged so as to be positionally displaced in the tire circumferentialdirection, and a groove portion 6 existing between the block landportions adjacent in the tire width direction extends so as to beoblique to the tire width direction and the tire circumferentialdirection. Yet further, a distance d₂ between the block land portionsadjacent in the width direction of the tire is shorter than a distanced₁ between block land portions adjacent in the circumferential directionof the tire. Yet further, as illustrated in FIG. 3, a length of theblock land portion 4 in the widthwise cross section of the tireincreases from both edge portions 7, 7 of the block land portion 4 inthe circumferential direction toward a central portion 8 of the blockland portion 4. Yet further, with respect to the block land portionarrays 5, 5 adjacent in the tire width direction, among side walls ofthe block land portion 4, an inclined angle α of a side wall 9 locatedon the groove portion 6 side between the block land portions adjacent inthe tire width direction with respect to the tire circumferentialdirection is larger than an inclined angle β of the other side wall 10located on the opposite side to said groove portion 6 as viewed from thetire width direction with respect to the tire circumferential direction.

The present inventor found that an increase in belt rigidity leads to adecrease in an area where a tread surface is brought into contact with aroad surface, and hence, shearing force in the circumferential directionof the tire excessively increases at the time of kick-out of the treadthat causes sliding wear to occur, which causes wear resistance toreduce. FIG. 4 shows a change in the shearing force (force acting in thedriving direction and on the contacting surface of the tire) acting inthe circumferential direction from the step-in time to the kick-out timeat given positions of the block land portion in a road-contacting statewhile the driving force is being applied, the change being plotted fromthe time when load by driving force is not applied to the tire. As shownin the solid line, in the conventional tire, at the step-in time, theshearing force in the circumferential direction is almost equal to theshearing force acting at the time when driving force is not applied, andthen, monotonously increases toward the kick-out time. The total amount(integral value of the shearing force in the circumferential directiongenerated from the step-in time to the kick-out time) of those forcesgenerated from the step-in time to the kick-out time makes a vehicleaccelerate, functioning as the force acting on a tire axis. If theground-contacting surface decreases, the decrease of the integral valueresulting from said decrease in the area is compensated with change inthe force per unit area being steeper from the step-in time to thekick-out time. As a result, the shearing force in the circumferentialdirection at the kick-out time increases, which reduces the wearresistance. The present inventor made a keen study on the basis of anidea that the integral value above can be compensated by generating theshearing force in the circumferential direction from the step-in time(change from the time when driving force is not applied) so as todecrease the shearing force in the circumferential direction at thekick-out time, as shown in the broken line in FIG. 4. As a result, it isfound that the characteristic shown in the broken line in FIG. 4 can beobtained by efficiently generating the force at the step-in time suchthat: as shown in FIG. 5, at the time when the driving force is applied,the shearing force is generated at a block land portion that has alreadybeen stepped in, causing the block land portion to deform; asdeformation by the shearing force increases, the block land portionrises accordingly, causing reaction at the next block land portion; thedeformation of the next block land portion increases as said next blockland portion is pressed on the road surface side. Although it is alsofound that this phenomenon effectively works by reducing a distancebetween the block land portions in the circumferential direction of thetire, the block land portions come into contact with each other at thetime when the tire is brought into contact with the road surface, in thecase where the distance between the block land portions in thecircumferential direction of the tire is too short, as illustrated inFIG. 6. This causes force to be generated in the same direction as thatof the driving force at the kick-out time, which adversely deterioratesthe wear resistance. The present inventor sought a configuration thatcan effectively utilize the action between the block land portions whileeliminating the effect caused by the contact between the block landportions in the circumferential direction of the tire, and as a result,found the configuration of the present invention. The present inventionis configured such that: between two block land portion arrays 5, 5adjacent to each other in the width direction of the tire, the blockland portions 4 constituting the block land portion arrays are arrangedso as to be positionally displaced from each other in the tirecircumferential direction; a groove portion 6 between block landportions adjacent to each other in the tire width direction extendsobliquely with respect to the tire width direction and the tirecircumferential direction; a distance d₂ between block land portionsadjacent to each other in the tire width direction is shorter than adistance d₁ between block land portions adjacent to each other in thetire circumferential direction, whereby it is possible to suppress anexpansion component (FIG. 6) of a rubber caused by the contact of theblock land portions 4, 4 adjacent to each other in the tirecircumferential direction, while effectively bearing the driving forceat the step-in time using reaction between the block land portions 4, 4by making the most of the configuration in which the groove portion 6between the block land portions adjacent to each other in the tire widthdirection extends obliquely with respect to the tire width direction andthe tire circumferential direction and the distance between the blockland portions is shorter. With this configuration, a gradient ofshearing force in the circumferential direction of the tire from thestep-in time to the kick-out time is made small, so that the slidingwear can be effectively suppressed.

The present inventor made a keen study on wear of the block land portionin the case where a tire having block land portions, in particular, atire for heavy load having a high aspect ratio is used in drive wheels,and as a result, found the following. More specifically, if the blockland portion is pressed against and is brought into contact with theroad surface in a horizontal manner, a stress caused byincompressibility of rubber is concentrated on a leading edge and atrailing edge of the block land portion as shown in FIG. 7( a). However,at the time of the kick-out time, tread wear occurs due to slippage ofthe tread portion, and the tread portion is pressed obliquely againstthe road surface because of existence of a belt, so that the stresscaused by the incompressibility of rubber is born by the central portionof the block land portion as shown in FIG. 7( b). In particular, in thecase where the tire has a high aspect ratio and high belt rigidity, thetread portion is further strongly pressed obliquely against the roadsurface, and as a result, the stress caused by the incompressibility ofrubber is further largely born by the central portion of the block landportion. The force accompanied by this compression and deformation isapplied in the same direction as the traveling direction of the vehicle,and is added with the driving force from the engine torque, which leadsto increase in the sliding wear. Therefore, by increasing the length ofthe block land portion in the widthwise cross section of the tire fromboth edge portions 7, 7 of the block land portion 4 in thecircumferential direction of the tire toward the central portion 8 ofthe block land portion 4 as described above, it is possible toconcentrate the compressive stress on the central area of the block landportion 4 as shown in FIG. 7( b) when the block land portion isobliquely brought into contact with the road surface. As a result, evenif there occurs a force that causes the rubber at the central area ofthe block land portion 4 to deform in the direction from the trailingedge 11 toward the leading edge 12, forces Q occur in a manner that wallportions of the block land portion 4 located on the trailing edge sideof the block land portion 4 and obliquely inclined with respect to thetire circumferential direction expand in the direction of the normal tosaid wall portions of the block land portion, as shown in FIG. 4. Atthis time, components R of the forces Q acting to expand are generatedfrom the right and the left wall portions of the block land portion 4and act in opposite directions to each other, and most of the componentsR are cancelled with each other within the block land portion 4, wherebythe other components P of the forces Q act against the force that causesthe rubber at the central area of the block land portion 4 to deformfrom the trailing edge 11 toward the leading edge 12. Therefore, theexcess deformation of the block land portion 4 is suppressed, whereby itis possible to prevent the partial wear and the sliding wear of theblock land portion 4. Further, as shown in FIG. 8, comparison was madebetween deformation (solid line) of a block land portion in the casewhere driving force is applied to the block land portion that does nothave the shape described above, and deformation (broken line) of a blockland portion in the case where driving force is applied to a block landportion 4 having the above-described shape and arrangement according tothe present invention. In the block land portion 4 according to thepresent invention, although deformation of the rubber toward thetrailing edge side of the block is suppressed at the step-in time due tothe same mechanism as that of the kick-out time, the incompressibilityof rubber causes the suppressed deformation to act in a direction inwhich the trailing edge 11 of the block land portion 4 that has beenalready stepped in is made further rise. This increases the shearingdeformation of a block land portion 4 to be stepped in next, therebyproducing a synergistic effect as shown in FIG. 4 in which the shearingforce at the step-in time increases and the shearing force at thekick-out time decreases, which has larger effect on the wear. Note that,at this time, a ratio of a length A of the block land portion 4 in thetire width direction at an edge portion in the tire circumferentialdirection with respect to a length B of the block land portion 4 in thetire width direction at the central portion 8 of the block land portion4 is preferably set in the range of 1:3 to 1:1.5. This is because it ispreferable to set the ratio of A to B in the range of 1:3 to 1:1.5, fromthe viewpoint of effectively suppressing the deformation of the blockland portion 4 in such a case where the block land portion 4 isobliquely brought into contact with the road surface, therebyeffectively suppressing the partial and the sliding wear of the blockland portion 4.

Further, the present inventor made a keen study on improving thetraction performance on the wet road surface while improving the partialwear resistance of the block land portion, and as a result, found thefollowing. More specifically, the present inventor found that it ispossible to increase the edge component by the side wall 9 to improvethe traction performance on the wet road surface while suppressing thepartial wear, by, among the side walls of the block land portion 4 atthe block land portion arrays 5, 5 adjacent in the tire width direction,setting the inclined angle α of the side wall 9 located on the grooveportion 6 side between the block land portions adjacent in the tirewidth direction with respect to the tire circumferential directionlarger than the inclined angle β of the other side wall 10 located onthe opposite side to said groove portion 6 as viewed from the tire widthdirection with respect to the tire circumferential direction. Note thatthe block land portion arrays 5, 5 adjacent in the tire width directionwork integrally, and hence the excess lateral force is not applied tothe side wall 9 located on the groove portion 6 side between the blockland portions adjacent in the tire width direction at the time when thetire is rotated with load, whereby the partial wear is less likely tooccur. Further, the present inventor found that, with the configurationdescribed above, even if the lateral force acts on the side wall 10 ofthe block land portion 4 at the time when the tire is rotated with loadsuch as during cornering, the stress does not excessively concentrate ona corner portion X of the side wall 10. This prevents the corner portionX from being the core of the partial wear and reduces the difference inrigidity in the circumferential direction within the block land portion4, whereby it is possible to improve the partial wear resistance.

At this time, the inclined angle β of the side wall 10 of the block landportion 4 with respect to the tire circumferential direction ispreferably in the range of 0 to 30°. This is because, in the case wherethe inclined angle β of the side wall 10 of the block land portion 4with respect to the tire circumferential direction exceeds 30°, thestress excessively concentrates on the corner portion X of the side wall10 at the time when the lateral force acts on the side wall 10 of theblock land portion 4 at the time when the tire is rotated with load, andhence, the corner portion X becomes the core of the partial wear. Thismay increase the rigidity difference within the block land portion 4 inthe circumferential direction, and cause the partial wear of the blockland portion 4. Further, it is more preferable that the inclined angle βof the side wall 10 of the block land portion 4 with respect to the tirecircumferential direction is in the range of 8 to 30°. This is becauseit is preferable to set the inclined angle β to 8° or more, from theviewpoint of the effect of preventing the partial wear obtained by theeffect of the force Q as illustrated in FIG. 3, as described above.

Further, it is preferable that the block land portions 4 adjacent in thetire width direction are arranged so as to be positionally displaced bya half pitch in the tire circumferential direction. This is because, bypositionally displacing the block land portions 4 by the half pitch, thedeformation force resulting from collapsing and deforming when the tireis rotated with load can be effectively transferred to a block landportion 4 adjacent in the tire width direction, and the driving forceper unit area that the tread portion 1 has to bear can be reduced,whereby it is possible to prevent the wear caused by the slidingphenomenon of the block land portions 4 with respect to the roadsurface. This makes it possible to reduce the gradient of the shearingforce in the tire circumferential direction from the step-in time to thekick-out time and also reduce the shearing force at the kick-out timethat causes the sliding wear, so that the sliding wear can be reduced.Note that the effect of the present invention can be obtained even ifthe block land portions 4 adjacent in the tire width direction arearranged so as to be positionally displaced not only by the half pitchbut also by other pitch in the tire circumferential direction. Further,from the viewpoint of further effectively suppressing the sliding wear,it is preferable that the inclined angle of the direction in which thegroove portion 6 between the block land portions adjacent in the tirewidth direction extends with respect to the tire circumferentialdirection is in the range of 15° to 70°. Further, from the viewpoint ofobtaining a mutual effect between the block land portions as describedabove and maintaining the effect until the end of the wear, it ispreferable for a depth of the groove portion 6 between the block landportions adjacent in the tire width direction to be in the range of 60to 100% of a groove depth of the circumferential groove 2A.

Further, it is preferable that, concerning the same block land portion4, the groove portion 6 located between block land portions adjacent inthe tire width direction and facing the same circumferential groove 2forms an open angle opening to the opposite direction to the tireequatorial plane CL as viewed from the tire circumferential direction.This is because, in the case where the groove portion 6 between theblock land portions adjacent in the tire width direction extends in onedirection, it is possible to effectively deal with an input from acertain one direction to prevent the sliding wear, but there is apossibility that the groove portion cannot effectively deal with aninput from other direction and cannot prevent the sliding wear. Further,the inclination of the extending direction of the groove portion betweenthe block land portions adjacent in the tire width direction is disposedso as to face the inclination of the block land portion 4 resulting fromthe shape in which the widthwise cross section of the tire at thecentral portion of the block land portion 4 increases. This makes itpossible to pattern the blocks without generating wasted spaces in thetire width direction, while effectively achieving the wear resistanceperformance without deteriorating any of the configuration and theeffects, whereby it becomes easy to implement patter designing bycombining with a second rib, shoulder rib, lug and the like.

Further, it is preferable that a ratio of the distance d₁ between theblock land portions adjacent in the tire circumferential direction withrespect to the distance d₂ between the block land portions adjacent inthe tire width direction is in the range of 1:0.85 to 1:0.3, and is morepreferably in the range of 1:0.7 to 1:0.4. In the case where the ratioof the distance d₁ between the block land portions adjacent in the tirecircumferential direction to the distance d₂ between the block landportions adjacent in the tire width direction exceeds 1:0.3, thedistance d₂ between the block land portions adjacent in the tire widthdirection is undesirably short even if the distance d₁ between the blockland portions adjacent in the tire circumferential direction issufficient. Therefore, the block land portions 4 adjacent in the tirewidth direction are brought into contact with each other when the tireis rotated with load; the deformation force resulting from collapsingand deforming cannot be effectively transferred to the block landportion 4 adjacent in the tire width direction; and, the shearing forcein the block land portion 4 cannot be effectively dispersed, possiblycausing the sliding wear. On the other hand, in the case where the ratioof the distance d₂ between the block land portions adjacent in the tirewidth direction to the distance d₁ between the block land portionsadjacent in the tire circumferential direction is less than 1:0.85, thedistance d₁ between the block land portions adjacent in the tirecircumferential direction is undesirably short even if the distance d₂between the block land portions adjacent in the tire width direction issufficient. Therefore, the block land portions 4 are brought intocontact with each other in the tire circumferential direction when theblock land portions 4 come into contact with the road surface, and thedeformation due to expansion of rubber illustrated in FIG. 6 occurs,possibly reducing the wear resistance.

Yet further, a ratio of the length d₃ of the block land portion 4 in thetire circumferential direction with respect to the distance d₁ betweenblock land portions adjacent in the tire circumferential direction ispreferably in the range of 1:0.25 to 1:0.05, and is more preferably inthe range of 1:0.17 to 1:0.07. In the case where the ratio of the lengthd₃ of the block land portion 4 in the tire circumferential directionwith respect to the distance d₁ between block land portions adjacent inthe tire circumferential direction exceeds 1:0.05, the block landportions 4 adjacent in the tire circumferential direction areundesirably close to each other when the block land portion 4 collapsesand deforms at the time of rotation of tire with load. Therefore, asillustrated in FIG. 6, when the block land portions 4 of the treadportion 1 that are in contact with the road surface are pressed anddeformed, the block land portions 4 adjacent in the tire circumferentialdirection are brought into contact with each other at the center of thetread portion 1; another block land portion 4 located outer than saidblock land portions 4 is pressed toward the outer side in the tirecircumferential direction; the block land portions 4 excessivelycollapse and deform in both a tire rotation direction and a directionopposite to the tire rotation direction. This increases a force actingat the trailing edge 11 in a direction in which the driving force isapplied, possibly causing the sliding wear resulting from saidcollapsing and deformation. On the other hand, in the case where theratio of the length d₃ of the block land portion 4 in the tirecircumferential direction with respect to the distance d₁ between theblock land portions adjacent in the tire circumferential direction isless than 1:0.25, the block land portions 4 adjacent in the tirecircumferential direction are undesirably departed from each other. Thismakes it impossible to utilize the shearing force at the trailing edge11 of the block land portion 4 to disperse the shearing force at theblock land portions 4 adjacent in the tire circumferential direction ina well-balanced manner, also possibly causing the sliding wear.

Yet further, the distance d₂ between the block land portions adjacent inthe tire width direction is preferably in the range of 1.0 to 5.0 mm,and is more preferably in the range of 1.5 to 3.5 mm. In the case wherethe distance d₂ between the block land portions in the tire widthdirection exceeds 5.0 mm, the distance d₂ between the block landportions adjacent in the tire width direction is undesirably long.Therefore, the deformation force resulting from collapsing and deformingcannot be transferred to block land portions 4 adjacent in the tirewidth direction. This causes the block land portion 4 to excessivelycollapse and deform in the tire circumferential direction, possiblycausing the wear resulting from the sliding of the block land portion 4.On the other hand, the distance d₂ between the block land portionsadjacent in the tire width direction is less than 1.0 mm, the distanced₂ between the block land portions adjacent in the tire width directionis undesirably short. Therefore, the block land portions 4 adjacent inthe tire width direction are brought into contact with each other whenthe tire is rotated with load, and the deformation force resulting fromthe collapsing and deforming cannot be effectively transferred to theblock land portion 4 adjacent in the tire width direction. This causesthe block land portion 4 to excessively collapse and deform, alsopossibly causing the wear resulting from the sliding of the block landportion 4.

Yet further, the distance d₁ between the block land portions adjacent inthe tire circumferential direction is preferably in the range of 3.0 to10.0 mm, and is more preferably in the range of 4.0 to 8.0 mm. In thecase where the distance d₁ between the block land portions adjacent inthe tire circumferential direction exceeds 10.0 mm, the distance d₁between the block land portions adjacent in the tire circumferentialdirection is undesirably long. Therefore, the road-contacting pressureat the block land portion 4 excessively increases, possibly reducing thewear resistance. On the other hand, in the case where the distance d₁between the block land portions adjacent in the tire circumferentialdirection is less than 3.0 mm, the distance d₁ between the block landportions adjacent in the tire circumferential direction is undesirablyshort. Therefore, the block land portions 4 are brought into contactwith each other in the tire circumferential direction at the time ofcoming into contact with the road surface, and deformation occurs due toexpansion of rubber as illustrated in FIG. 6, possibly reducing the wearresistance.

Yet further, as illustrated in FIGS. 9 and 10, it is preferable that theblock land portion 4 is provided with a narrow groove 13 communicating,in the tire width direction, the two circumferential grooves 2, 2adjacent to said block land portion 4. By providing an additionaltrailing edge 11 as described above, it is possible to generally improvethe gripping force at the block land portion 4. Therefore, it ispossible to efficiently convert the torque from the engine into thedriving force. Note that, at this time, the narrow groove 13 may becurved or bent within the block land portion 4.

Further, it is preferable for the narrow groove 13 to open to thecircumferential groove 2 at the central portion 8 of the block landportion 4. This is because, if the narrow groove 13 opens at a regionother than the central portion 8 of the block land portion 4, thegripping force serving as the driving force cannot be dispersed in awell-balanced manner within the block land portion 4, and hence, thereis a possibility that the torque from the engine cannot be efficientlyconverted into the driving force.

Yet further, it is preferable for the length of the narrow groove 13 inthe tire circumferential direction to be in the range of 5 to 20% of adepth of the lateral groove 3 (depth in a radial direction), and morepreferably be in the range of 7 to 18%. In the case where the length ofthe narrow groove 13 in the tire circumferential direction is less than5% of the depth of the lateral groove 3, the length of the narrow groove13 in the tire circumferential direction is undesirably short. As aresult, similar to a case where the block land portion 4 is not providedwith the narrow groove 13, the gripping force decreases from the leadingedge 12 toward the trailing edge 11, and hence, there is a possibilitythat the effect obtained by disposing the narrow groove 13 does notwork. On the other hand, in the case where the length of the narrowgroove 13 in the tire circumferential direction exceeds 20% of the depthof the lateral groove 3, the length of the narrow groove 13 in the tirecircumferential direction is undesirably long. As a result, the forceresulting from the reaction between the block land portions 4, each ofwhich is separated by the narrow groove 13 in the block land portion 4,cannot be transferred, causing the block land portion to excessivelycollapse and deform, and possibly causing the sliding wear resultingfrom this. Further, in order to maintain the sufficient effect until theend of the wear, it is preferable for the depth of the narrow groove 13to be in a range of 60 to 100% of the depth of the lateral groove 3.

Further, it is preferable for the length d₃ of the block land portion 4in the tire circumferential direction to be in the range of 1.0 to 2.5%of a circumferential length of the tire. In order to effectively obtainthe above-described effect of the block land portion 4 according to thepresent invention, it is appropriate that the length d₃ of the blockland portion 4 in the tire circumferential direction is less than orequal to 2.5% of a circumferential length of the tire. This is because,in the case where the length d₃ of the block land portion 4 in the tirecircumferential direction exceeds 2.5% of the circumferential length ofthe tire, the rigidity against shearing force of the block undesirablyincreases, and hence there is a possibility that the block land portion4 that has already been stepped in does not sufficiently rise in amanner described above. On the other hand, in the case where, althoughthe length d₃ of the block land portion 4 in the tire circumferentialdirection is less than or equal to 2.5% of the circumferential length ofthe tire, the length d₃ is less than 1.0%, the rigidity of the blockland portion 4 is undesirably low. Thus, in such a case, when thedriving force is applied to the block land portion 4, the block landportion 4 excessively shears and deforms, and hence, the sliding wearcannot be sufficiently suppressed. Accordingly, by setting the length d₃of the block land portion 4 in the tire circumferential direction to bein the range of 1.0 to 2.5% of the circumferential length of the tire,it is possible to secure the rigidity of the block land portion 4, andthe effect of the block land portion 4 described above can be achievedeffectively, whereby it is possible to prevent the wear resistance fromdeteriorating.

It should be noted that the description above is only a part of theembodiment of the present invention, and it may be possible to combinethese configurations with each other or apply various modificationswithout departing from the gist of the present invention. For example,in tires having the configurations illustrated in FIGS. 2, 9 and 10, twoblock land portion arrays 5 form one unit, and plural units of the blockland portion arrays 5 are arranged on the surface of the tread portion,thereby obtaining the effect of preventing the partial wear according tothe present invention. However, the number of unit may be one, and itmay be possible to form the one unit by three or more block land portionarrays 5 and arrange them on the surface of the tread portion.Alternatively, as illustrated in FIG. 11, rib-like land portions 14 maybe provided on the shoulder sides of the tread portion 1, and, theabove-described configurations of the present invention may be employedfor the block land portion arrays 5 between the rib-like land portions14; further, as illustrated in FIG. 12, block land portion arrays 5formed by rectangular-shaped land portions 4 may be provided on theshoulder sides of the tread portion 1, and the above-describedconfigurations of the present invention may be employed for block landportion arrays 5 between the rectangular-shaped block land portionarrays 5; further, as illustrated in FIG. 13, block land portion arrays5A formed by rectangular-shaped block land portions 4 and block landportion arrays 5B formed by hexagonal-shaped block land portions 4 maybe provided on the shoulder sides of the tread portion 1, and theabove-described configurations of the present invention may be employedfor block land portion arrays 5 adjacent to each other between the blockland portion arrays 5B, the block land portion arrays 5 being on thetire equatorial plane side; and, various tread patterns are possible,provided that the tread portion has the configurations according to thepresent invention. Alternatively, from the viewpoint of improving thepartial wear resistance while maintaining the effect obtained by thepresent invention, it may be possible to form a corner portion of theblock land portion 4 in a chamfered shape in adjacent block land portionarrays 5 located on the tire equatorial plane CL side and employing theconfigurations according to the present invention, as illustrated inFIG. 14. Further, although not illustrated, it is possible to form theside walls 9, 10 of the block land portion 4 in a curved shaped so as tohave a curvature while maintaining the effect obtained by the presentinvention.

EXAMPLE

Next, as samples of pneumatic tires for heavy load having a size of495/45R22.5, there were prepared a pneumatic tire (Conventional Exampletire) having a tread pattern according to the conventional technique,pneumatic tires (Comparative Example tires 1 to 9) each having aconfiguration similar to the pneumatic tire according to the presentinvention, and pneumatic tires (Example tires 1 and 2) according to thepresent invention, and performance evaluation was made for those tires.Details of the evaluation will be described below.

The Conventional Example tire has block land portions having arectangular shape as illustrated in FIG. 15, and has characteristicsshown in Table 1. The Comparative Example tires 1 to 9 haveconfigurations illustrated in FIG. 16 through FIG. 24, respectively, andhave characteristics shown in Table 1. The Example tires 1 and 2 havetread portions corresponding to those illustrated in FIG. 2 and FIG. 25,respectively, and are pneumatic tires having block land portionsarranged on the entire tread portion thereof. Further, between blockland portion arrays adjacent to each other, block land portionsconstituting the block land portion arrays are arranged so as to bepositionally displaced by a half pitch from each other in the tirecircumferential direction. Yet further, a groove portion 6 between blockland portions adjacent to each other in the tire width direction extendsobliquely with respect to the tire circumferential direction; a distancebetween block land portions adjacent to each other in the tire widthdirection is shorter than a distance between block land portionsadjacent to each other in the tire circumferential direction. Still yetfurther, among side walls of a block land portion in block land portionarrays adjacent in the tire width direction, an inclined angle of a sidewall located on the groove portion side between the block land portionsadjacent in the tire width direction with respect to the tirecircumferential direction is set larger than an inclined angle of theother side wall located on the opposite side to said groove portion asviewed from the tire width direction with respect to the tirecircumferential direction, and characteristics thereof are shown inTable 1.

TABLE 1 Conven- Compara- Compara- Compara- Compara- Compara- Compara-tional tive tive tive tive tive tive Example Example Example ExampleExample Example Example tire tire 1 tire 2 tire 3 tire 4 tire 5 tire 6Corresponding FIG. 15 FIG. 16 FIG. 17 FIG. 18 FIG. 19 FIG. 20 FIG. 21drawing Length of block 60.0 mm 60.0 mm 60.0 mm 60.0 mm 60.0 mm 60.0 mm60.0 mm land portion in tire circumferential direction Length in tire40.0 mm 19.0 mm 27.0 mm 27.0 mm 27.0 mm 16.0 mm 18.0 mm width directionof edge portion of block land portion in the tire circumferentialdirection Length in tire 40.0 mm 38.0 mm 27.0 mm 20.0 mm 33.0 mm 38.0 mm40.0 mm width direction of edge portion of block land portion in tirecircumferential direction Depth of lateral 18.0 mm 18.0 mm 18.0 mm 18.0mm 18.0 mm 18.0 mm 18.0 mm groove Distance between 10.0 mm 10.0 mm 3.0mm 3.0 mm 3.0 mm 3.0 mm 0.8 mm block land portion adjacent in tire widthdirection Depth of groove 15.0 mm 15.0 mm 15.0 mm 15.0 mm 15.0 mm 15.0mm 15.0 mm portion between block land portion adjacent in tirecircumferential direction Distance between 7.0 mm 7.0 mm 7.0 mm 7.0 mm7.0 mm 7.0 mm 7.0 mm block land portion adjacent in tire circumferentialdirection Inclined angle of 0°/0° 20°/−20° 20°/20° 20°/0° 20°/0°20°/−20° 20°/−20° side wall of block land portion with respect to tirecircumferential direction (α/β) Presence/absence Not exist Not exist Notexist Not exist Not exist Not exist Not exist of narrow groove Width ofnarrow — — — — — — — groove Depth of narrow — — — — — — — groovePresence/absence — — — — — — — of bent of narrow groove Number of block— — 2 2 2 2 2 land portion adjacent in tire width direction Compara-Compara- Compara- tive tive tive Example Example Example Example Exampletire 7 tire 8 tire 9 tire 1 tire 2 Corresponding FIG. 22 FIG. 23 FIG. 24FIG. 2 FIG. 25 drawing Length of block 60.0 mm 60.0 mm 60.0 mm 60.0 mm60.0 mm land portion in tire circumferential direction Length in tire16.0 mm 16.0 mm 30.0 mm 16.0 mm 17.0 mm width direction of edge portionof block land portion in the tire circumferential direction Length intire 38.0 mm 38.0 mm 61.0 mm 40.0 mm 38.0 mm width direction of edgeportion of block land portion in tire circumferential direction Depth oflateral 18.0 mm 18.0 mm 18.0 mm 18.0 mm 18.0 mm groove Distance between3.0 mm 3.0 mm 1.8 mm 3.0 mm 3.0 mm block land portion adjacent in tirewidth direction Depth of groove 15.0 mm 15.0 mm 15.0 mm 15.0 mm 15.0 mmportion between block land portion adjacent in tire circumferentialdirection Distance between 7.0 mm 7.0 mm 4.0 mm 7.0 mm 7.0 mm block landportion adjacent in tire circumferential direction Inclined angle of20°/−20° 20°/−20° 27°/−27° 23°/−20° 20°/−18° side wall of block landportion with respect to tire circumferential direction (α/β)Presence/absence Exist Exist Exist Not exist Not exist of narrow grooveWidth of narrow 1.0 mm 1.0 mm 1.0 mm — — groove Depth of narrow 15.0 mm15.0 mm 15.0 mm — — groove Presence/absence Not exist Exist Exist — — ofbent of narrow groove Number of block 2 2 5 2 2 land portion adjacent intire width direction

Each of the sample tires described above was assembled with a rim of17.00×22.5 to form tire wheels, and were mounted to a tractor vehiclefor use in tests as driving wheels. These sample tires were inflated ata pressure of 900 kPa (relative pressure), load mass of 57 kN wasapplied to the tires, and various evaluations as described below weremade.

As for the wear resistance, the amount of wear at the central portion ofthe block land portion was measured after traveling 50000 km on a testroad. With the amount of wear of the central portion of the block landportion of the Conventional Example tire being set to 100 as index,relative values were obtained for the other tires, and the evaluationwas made by comparing the obtained relative values. Note that thesmaller index value represents the better wear resistance. Table 2 showsthe results thereof.

As for the partial wear resistance, the wear difference between thecentral portion of the block land portion and the outside portionthereof in the tire width direction was measured after traveling 50000km on a test road. With the wear difference of the Comparative Exampletire 5 being set to 100 as index, relative values were obtained for theExample tires 1 and 2, and the evaluation was made by comparing theobtained relative values. Note that the smaller index value representsthe better partial wear resistance. Table 2 shows the results thereof.

As for the traction performance on the wet road surface, measurement wasmade on time required for the vehicle described above to travel 15 m atthe time when, using a test course having a metal plate placed thereon,the vehicle starts on the wet road surface with a water film of 2 mmwhile keeping the engine speed constant. Then, with the accelerationperformance of the Comparative Example tire 5 being set to a referencevalue as index, relative values were obtained for the Example tires 1and 2 and the evaluation was made by comparing the obtained relativevalues. Note that the larger value represents the better tractionperformance on the wet road surface. Table 2 shows the results thereof.

TABLE 2 Traction Corre- Partial performance sponding Wear wear on wetroad drawing resistance resistance surface Conventional FIG. 15 100 — —Example tire Comparative FIG. 16 93 — — Example tire 1 Comparative FIG.17 83 — — Example tire 2 Comparative FIG. 18 83 — — Example tire 3Comparative FIG. 19 79 — — Example tire 4 Comparative FIG. 20 76 100 100Example tire 5 Comparative FIG. 21 86 — — Example tire 6 ComparativeFIG. 22 71 — — Example tire 7 Comparative FIG. 23 74 — — Example tire 8Comparative FIG. 24 67 — — Example tire 9 Example tire 1 FIG. 2 77 100102 Example tire 2 FIG. 25 77  98 100

As can be clearly understood from the results shown in Table 2, theExample tires 1, 2 and the Comparative Example tires 1 to 9 exhibitimproved wear resistance as compared with the Conventional Example tire.Further, as a result of comparison of the Example tires 1 and 2 with theComparative Example tire 5 having the configuration same as the Exampletires 1 and 2 except that the inclined angle of the side wall of theblock land portion falls outside the range of the present invention, itcan be known that all the tires exhibit the same wear resistance. As forthe partial wear resistance, the Example tire 2 improves as comparedwith the Conventional Example tire 5. As for the traction performance onthe wet road surface, the Example tire 1 improves as compared with theComparative Example tire 5.

INDUSTRIAL APPLICABILITY

As can be clearly understood from the description above, according tothe present invention, it is possible to provide a tire exhibitingimproved wear resistance, partial wear resistance and tractionperformance on the wet road surface, by optimizing the shapes of theblock land portions and positional arrangement thereof.

EXPLANATION OF REFERENCE CHARACTERS

-   -   1 Tread portion    -   2, 2A Circumferential groove    -   3 Lateral groove    -   4 Block land portion    -   5 Block land portion array    -   6 Groove portion between block land portions adjacent in the        tire width direction    -   7 End portion of block land portion in the tire circumferential        direction    -   8 Central portion of block land portion    -   9, 10 Side wall of block land portion    -   11 Trailing edge    -   12 Leading edge    -   13 Narrow groove    -   14 Rib-like land portion

1. A tire having, on a tread portion, a plurality of circumferentialgrooves extending in a tire circumferential direction, and plurallateral grooves each communicating adjacent two circumferential grooves,thereby defining a plurality of block land portion arrays formed by alarge number of block land portions, wherein: between block land portionarrays located adjacent to each other while sandwiching thecircumferential groove, the block land portions constituting said blockland portion arrays are arranged so as to be positionally displaced fromeach other in the tire circumferential direction; a groove portionbetween the block land portions adjacent in the tire width directionextends obliquely with respect to the tire width direction and the tirecircumferential direction; a distance between the block land portionsadjacent in the tire width direction is shorter than a distance betweenthe block land portions adjacent in the tire circumferential direction;a length of the block land portion in the widthwise cross section of thetire increases from both edge portions of the block land portion in thecircumferential direction toward a central portion of the block landportion; and, among side walls of the block land portion in block landportion arrays adjacent in the tire width direction, an inclined angleof a side wall located on the groove portion side between the block landportions adjacent in the tire width direction with respect to the tirecircumferential direction is larger than an inclined angle of the otherside wall located on the opposite side to said groove portion as viewedfrom the tire width direction with respect to the tire circumferentialdirection.
 2. The tire according to claim 1, wherein an inclined angleof the side wall located on the outside of the block land portion in thetire width direction with respect to the tire circumferential directionis in the range of 0 to 30°.
 3. The tire according to claim 1, wherein adistance between the block land portions adjacent in the tirecircumferential direction with respect to a ratio of a distance betweenthe block land portions adjacent in the tire width direction is in therange of 1:0.85 to 1:0.3.
 4. The tire according to claim 1, wherein alength of the block land portion in the tire circumferential directionwith respect to a ratio of a distance between the block land portionsadjacent in the tire circumferential direction is in the range of 1:0.25to 1:0.05.
 5. The tire according to claim 1, wherein the distancebetween the block land portions adjacent in the tire width direction isin the range of 1.0 to 5.0 mm.
 6. The tire according to claim 1, whereinthe distance between the block land portions adjacent in the tirecircumferential direction is in the range of 3.0 to 10.0 mm.
 7. The tireaccording to claim 1, wherein the block land portion is provided with anarrow groove communicating two circumferential grooves adjacent in saidblock land portion in the tire width direction.
 8. The tire according toclaim 7, wherein the narrow groove is open to the circumferential grooveat the central portion of the block land portion.
 9. The tire accordingto claim 7, wherein the length of the narrow groove in the tirecircumferential direction is in the range of 5 to 20% of a depth of thelateral groove.